Process of recovering indium



Patented Dec. 30, 1947 PROCESS 0F RECOVERING INDIUM Yuri E. Lebedcff, Metuchen, N. J., assigner to 'American Smelting and Refining Company,

New York, N. Y., a corporation of New Jersey Application March 17, 1944, Serial No. 526,978

1 This invention relates toa process for recovering indium from metals or alloys such as lead, zinc and the like. Y

Methods have been developed heretofore for treating indium-containing metals to recover indium which comprise heating the metal with caustic soda and niter to selectively oxidize the indium whereby it can be removed and recovered. When appreciable amounts of zinc or other impurities such as Sn, As, Sb, Te, etc. are present, however, the caustic-niter fusion process is not ei'iective in bringing about a clean-cut selective separation of indium from these impurities.

According to the present invention a method is provided for removing indium from impure 11 Claims.

l lgible.

metals or alloys particularly zincky lead metal containing indium by converting the indium into indium chloride. A melt of the metal containing indium is treated with a suitable chlorine supplying agent or gaseous chlorine to selectively remove the zinc and indium as chlorides using a low melting cover slag and temperatures sufficiently low to avoid loss of indium by volatilization.

The accompanying drawing illustrates by means of a ow sheet the various steps of my new process. It will be observed that the process includes reacting the melt containing indium with a chloridizing agent in the presence of a low melting flux or slag whereby substantially all of the indium is converted to indium chloride which enters the slag phase. The pyrometallurgical process is carried out Without appreciable loss of indium due to volatilization by the use of a low melting chloride cover slag. After the melt has been suiiiciently chloridized the slag is drawn oi and treated to recover indium as metallic indium of high purity.

Inasmuch as indium chloride (InCls) begins to volatilize when heated above 750 F. and rapidly fumes oli at 850 F. and above, under ordinary atmospheric pressure conditions, it was found necessary, in order to prevent volatilization losses of indium during treatment of the melt with a molten chloride slag, to employ a slag which would fuse at temperatures below that at 4which indium chloride would be lost as fume. Attempts to use lead chloride alone as the slag forming constituent were unsatisfactory because tempera: tures around 950 F. Were required to produce a workable slag for reacting with the melt. At this high temperature excessive loss of indium by volatilization resulted. v

It was found, however, that if lead chloride was reacted with the molten lead metal in the pres# ence of low melting salts, such as zinc chloride or a eutectic mixture of rzinc chloride and sodium chloride, the melting temperature of the resulting slag could be kept sufficiently low so that the loss of indium by Volatilization was practically neg-lv during the process.

The function of the chlorides employed in treating the indium-containing melt was fourfold, (l) to provide the chloridizing agent, (2) to lower the fusion temperature of the resulting slag, (3) to decrease the concentration of the indium chloride in the slag by dilution and (4) to cover and prevent the metal of the melt from coming directly into contact With air during the process which is conveniently carried out as an open kettle operation. As slag forming agents I have found zinc chloride and sodium chloride to be entirely satisfactory. Further, by employing a suitable mixture oi these low melting slag forming substances I have found that the recovery of indium is enhanced during the subsequent treatment of the slag, This treatment involves leaching the indium chloride slag with dilute sulphuric acid and precipitation of the dissolved indium by means of zinc dust.

Removal of indium from the melt with lead chloride is an equilibrium reaction. When the reaction is carried out at temperatures below 775 F. in the presence of diluent slags, loss of indium by volatilization is avoided but the completeness of indium removal from the metal phase is a function of the concentration of lead chloride in the nal slag. Equilibrium of the reaction between the two phases (metal and slag) is usually attained in a few minutes when the molten phases are intimately mixed together. I have observed as the result of tests that an equilibrium exists between a liquid slag containing about 13% In, 20% Zn, 17% Pb all as chlorides including some sodium chloride and a lead metal bath (zinc free) containing 0.25% indium at about 725 F, under ordinary atmospheric pressure conditions.

To lower the indium content of the metal phase below 0.25% a greater concentration of lead Chloride in the slag is required. However, the addition of large amounts of lead chloride is objectionable due to the formation of greater quantities of lead sulphate residue during the subsequent step of leaching with a correspondingly greater retention of'soluble indium chloride in this insoluble residue. Accordingly, I prefer to resort to a countercurrent system which permits me to restrict the addition of lead chloride as a slag forming constituent whereby a high grade (l0 to 14% In) indium chloride slag is formed After skimming this high indium slag from the kettle, the treated metal left generally contains from 0.20 to 0.30% indium. The zinc content of the treated metal phase at this stage is substantially nil.

To remove this residual 0.20 to 0.30% indium, the` metal is 'preferably'reacted with additional quantities of'lead chloride (or chlorine gas) in the presence of diluent slags, such as ZnClz', MgCl2, KCl and NaCl eutectic mixtures to provide afuid slag at temperatures less than 800 F.

This slag is much lower in indium than the initial high indium slag j and f accordingly-f the tempera;- ture employed-may be somewhat higher than 7759 F. as used in the rst chloride treatment step.

The low grade indium chloride slag produced ini. this instance is returned to thesystem, being...

added to the next batch of lead `metal to be treated as shown on the drawing flowisheeti The zinc and indium contentof the metal which s".

is treated with the returned slag.I determines;

Whether additional lead chloride andor. zinc..V

chloride are required in order to properly balance the reaction. If the original metal contains non.

zinc, metallic zinc may be added to react with the lead chloride-in the return slag which isin excess ofi-*the amountnecessary forindium removal, forming. apart or all of the zinc chloride needed.

As any alternativemethod for removing the residual. indiurnlef-t in the metal phase after removal of-vfthe high-indium chloride slag, the metal mayfbetreatedwith caustic and sodium nitrate. Inasmuch as.zinc-has.been removed by th e.-initial 'lead chloride-.treatment there. is no inter-ference by-zinc.- However, if the metal containsgrelativelylarge amounts, of antimony; arsenic, tin or A tellurium.. asf impurities this caustic-niter method Vis ymuchless f suited because of theelack.-.of selectivity between. indiumand these timpur-ities as` previouslyexplained. In lthis respect .the -chloride method'vpossesses .a marked advantage-over the. caustic-.niter procedureA described; Wheretheindium .containing metal to -be processed is suiiiciently low crime-from these impurities the. latter method may.. however. be used kas indicated` in. dotteddines. onthe drawing iiow sheet.

TheA procedure. for practicing my invention is illustrated by the following.speeicc examples.:

ErampleA I IndiumbeaIing-.lead in;;the, amount of 50,330 lbssandassaying0.96%. In, 0.95% ZnV and 0.10% Sn ,but .substantially .freefrom. other impurities, i.-,e. Cu,A Bi,` Sb, As,.Te,. Ag and. Tl was. .placed in. a.kettle andv melted.. To this meltwas added 3000lbs. of. lead .chloride .and. 300. lbs. .of sodium chloride,l the. chlorides beingdntroduced ontothe surfacef the. melt..,which wasmaintainedat avtemperature.` of between..710 and-.720

After mixingjhe Afused...chlorides into the melt for minutes,`v the stirringwasstopped and the chloride slagskimmed .from .the surfaceof the melt.. vThe...chlc ,ride slag weighed 2308.1bs. and assayed 13.7%... indium, 20.1%.. zinc .and 18.7% leadas principal constituents. The treatedlead meter remaining .after Vsliimmirigpf .the indium chloride ,slagcontained 0.30% indium but was freeirom zinc...y ToremQvethe residual indium theleadmetaiwas heated to .about 840 F. to form treated with 0 lbs, ,moreofg caustic ,(NaOH) andsmbs.orniter.and aftermixins. foren additional L2 .hours and 40 minutesthe lead: metal wasfoundtoeontain no indium. Caustic slag skimmed.from...the.melt .weighed 239.5 lbs. and assayed 6.43.%. .indum... The treated lead metal remaining which was free from indium amounted to 50,800 lbs. was transferred to the lead refinery to. remove small amountsioibismuth:and dor.

To recover the indiumv from' thefchloride slag produced by treating the melt with chloride salts the slag weighing 2308 lbs, was placed in a leachimg .tankandleached with aqueous H2804 containing 39710" lbs. sulphuric acid and 82.0 cu. ft. ofwater.v After -leaching with agitation at 158- 16.7'C.` thef.leached mass was cooled to 72 F.

and Yi'llterediandthe residue washed with water.

The filtrate` solution was controlled so as to contain approximately 45 gms/liter of H2804 and analyzed'.` 50 gms/liter of indium, Inasmuch as the Volume of the solution measured 98.0 cu. ft., .the amount vof .indium-in .solution totaled :about 303.6 lbs. To. this. filtrate `solution was added 415 lbs. of zinc dust and the mixture agitated while the .temperature wasmaintainedat F. to precipitatethefindium from thesolution as aspongy-mass.-

After precipitation .of the-indium the solution was liiltered and the filtrate being-practically free of indium (0.02%) vwas discarded.A Sponge indium retained on `the filtercloth was-pressed and thendigested atf320 110.3749 F. with caustic, using.175.0 .lbs-NaOH-.and 46.0 lbs. water. Following digestion ofthe spongevindiumwith caustic solution theclear solution was l-decanted and the remainder passed; toA a lter pressto `recover the residue which:.was returned to thexinitial -leachingjtankfor.,recycling..` The caustic ltrate was found tocontainno Vindium andA wasfdiscarded.

Crudeindium 1metal .recovered after digesting with caustic solution.. weighed 310 lbs. and assayed .97.5 .Im-0.5 %.,Zn',. ,approximately 1 Tl, approximately..0.5%Pb,..0.03% Sn, 0.01% Sb. To.;.produce -renedindium this crude indium metal was melted in an iron kettle to about 500. F. and chemically pure zinc chlorideadded in the amount. of approximately.7% by weight ofthe metaltreated. and. thereafter v15 lbs. of chlorine gaswas reacted ,Withfthe melt at temperature of 3509,-39092 F. Upon removingthe slag indium metal .of 99.55 purity Ewas .obtained which. was substantially, free of thallium and impurities whichnwould interfere. with electrolysis of the indium. metal.. Using. this indium metal` as anodes electrolysis-was carried. Lout Vproducing a final .indium -metalanalyzing 99.9+% pure indium. Preferably an. f acid.. sulphate electrolyte is gused. A suitable electrolyte comprises an aqueous sulphuric acid solution.- containing about 10 .gms/liter of. sodium- .sulphate and. having a p I- I'valueof between 1.8 and-2.2..

Example II Indium; bearing zincky lead in' the amount of 10,0.rlbs. andassaying 0.85 %In; 0;90%"Zn, Sn 1.5% and 'additional small amountsof Sb, As, Bi, Cu and 'Ag was melted in a kettle." To this melt .was added 9.2 lbs. of indiumchloride slag returned from previous charge for'recyclingcontaining In, Zn,:Pb and Na .chloride complexes; This slag was addedto the surface Vof themelt and fused forming a cover slag which'was gradually stirred into the melt without exposing the metal surface to air oxidation, the melt being-heldA at a temperature-between 725; and 750 during the treatment.

AfterV mixing' the 'melt and slag A-for 'approximately 45 minutes stirring was-stopped and the slag skimmed from the melt.A The slag produced weighed '7.'7 lbs. `and assayedj10.8 %V In, 29.1%Zn and 13% Pb asY the `principaln constituents-f This indium 'chloride 'slag wasfthen treated to recover metallic indium' as described in Example I.

The treated metal remaining after removal of the indium chloride slag and amounting to about 100 lbs. contained no zinc and only 0.20% indium.

This metal has reheated to 735 F. and treated with a mixture comprising 6 lbs. of lead chloride, 3 lbs. zinc chloride and 0.5 lb. sodium chloride. After melting and intermixing this chloride slag with the melt for about 45 minutes without unduly exposing the metal surface to air oxidation and while maintaining the temperature of the melt to between 725 and 750 F. the mixing was stopped and the slag skimmed oiT. The skimmings weighed 9.2 lbs. and comprised a low grade that when sufcient amount of zinc is present the chloride may all be introduced as PbClz and NaClinasmuch as ZnClz' will be formed during the ensuing reaction. Likewise other sufficiently low melting slag forming salts, i. e. Zn, Pb and Na chlorides may be employed in practicing my process. For example, suitable mixtures of MgCl2, KCl or NaCl and the like may be substituted for my preferred slag forming substances. All that is necessary is to use proper proportions of a chloride reagent and flux such that the resulting mixture will melt at a suilciently low temperature and react with the indium in the melt forming indium chloride without incurring volatilization losses of indium which result when the melt is overheated as explained. It will be understood, of course, that where the chlorine supplying substanceused has suiiiciently low melting properties the addition of ux may be omitted.

As an alternative procedure for chloridizing the metal, the indium containing melt may be pro- .vided with a suitable cover slag and the indium reacted with chloride by introducing gaseous chlorine into the molten mass at the proper temperature whereby indium is united with chlorine to form indium chloride which enters the slag phase,

and is separated from the body of the melt as described.

The present process oiers many important advantages over prior methods. It is economical to operate and requires no special equipment, the process being adapted to be carried out in an open kettle without fume collecting apparatus. Moreover, the invention provides a commercially practical and efcient method of treating metals containing indium to recover the indium as metal of high purity.

While I have described the invention by way of specific examples, it will be understood that various changes, substitutions `and omissions may be made by those skilled in the art without departing from th'e spirit andv scope of my invention as defined in the annexed claims.

' What is claimed is:

1. Aprocess for separating indium from indium-containing leadv metal andA lead alloys whichl comprises establishing a molten bath of the material to be treated, introducing slag forming ingredients including a chloridizing agent in the molten bath and stirring the slag into the melt to cause the indium to react with said chloridizing agent and form indium chloride, said slag be- 6 ling s'uiliciently low melting to produce a liquid cover slag for said molten bath at temperatures below that at which indium chloride volatilizes and escapes as fume, and separating the thus formed indium chloride from the surface of the melt as a slag constituent.

2. A process for separating indium from indium-containing lead metal and lead alloys which comprises heating said material to form a melt,

introducing a low melting chloride flux and chlorine supplying reagent onto the surface of the .Y melt and fusing said flux and reagent to produce a chloride slag for said melt, said slag being sufficiently low melting to produce a liquid slag at temperatures below that at which indium is lost by fuming, intermixing the chloride slag and melt Without excessive exposure of the metal to air to cause the indium present in the melt to react with said chloride slag and form indium chloride, thereafter separating said indium chloride-containing slag and leaching same to selectively dissolve the indium chloride, and treating the leach solution containing indium chloride to f precipitate the indium.

3. A process for separating indium from indium-containing lead metal and lead alloys which comprises establishing a molten bath of the material to be treated, introducing slag forming in- 'aqueous sulphuric acid, precipitating the indium from the leach solution with zinc dust, and treating the precipitated indium metal to remove the zinc as zinc chloride and produce indium metal which is substantially free of impurities.

4. A process for separating indium from indium-containing lead metal and lead alloys which comprises establishing a molten bath of the material to be treated, introducing slag forming ingredients including a chloridizing agent in the molten bath to cause the indium vto react therewith and form indium chloride, said slag being suliciently low melting to produce a liquid cover slag for said molten bath at temperatures below that at which indium chloride volatilizes and escapes as fume, separating the slag from the melt,

leaching said slag with an aqueous sulphuric acid solution containing approximately 45 grams per liter of sulphuric acid to dissolve the indium chloride contained in said slag, said leaching being carried out by intermixing said slag and sulphuric acid solution heated to between and 185 F., thereafter cooling the mixture to about 70 F. and

filtering the solution from the residue, heating remove caustic and returning the residue to the sulphuric acid leaching step, recovering crude indium metal after treatment with caustic solution Vand treating the same to remove thallium by establishing a melt of said crude metal, introducing chemically pure zinc chloride and chlorine gas into said melt to react with the thallium and form thallium chloride and a zinc chloride slag Y I'nixture,` separating said :zinc-chlor-iderand thal lium chloride containing :slag fromgztheL-*meltto Y'recover a relativelyv pure .indium-metal.

5. In the process vof rrecovering indium from 'indium-bearing metal material containing-lead and zinc the steps whichcompriseestablishing a rmelts of-said material, .addingaglead chlorideflux ymixture thereto, saidy `chloride andv ux vbeing introduced iny proportionate amounts -such that theresulting mixture will melt:.and form-a coverk slag-for the melt ata temperaturepbelow that at v* which substantial loss of. indiumby volatilization from said melt occurs,- reacting said mixture with lthe melt to convert the' indium` into indiumchloiride,r and separatingfthexslag which includes the- `indium `chloride from the melt.

6;' In the process of recoveringrindiumirom zincky indium-bearing lead-metal they steps which comprise establishing a melt -of the indium-bear ing metal, introducing na chloridizing mixture mixture will melt and forma cover slagffor said vmelt at temperaturessuiciently below that at which indium is lost` by volatilization, and intermixing the chloride'slag and melt to reactzthe chloride with the indium and convert the indium of the melt into indium chloride.

7. The process of recovering indiumfrom-n indium-bearing lead vmetal lwhich comprises establishinga melt of the indium-bearing metal,

`introducing a mixture of lead chloride, Zinc #chloride and sodium chloride into-said melt to form a low melting chloridizing slag `for said melt, :said chloride constituents being introduced in proportionate amounts such that the resulting s mixture will melt and form a cover slag for said melt at temperaturesbelow that at which indium begins to fume off from the melt, reacting said chloridizing slag with the melt bystirring the same together while the melt is heated to a temperature between about '700 and 750 F., sepa- -rating the resultant chloride slag from the melt .and recovering the indium chloride from the chloride slag by dissolving the indium chloride in sulphuric acid solution and ltering the solution .to remove the insoluble residue.

8. In the recovery of indium from indiumy. bearing lead containing appreciable amounts of Zn, As, Sb, and Te as impurities, the steps which consist in establishing a melt of` such indiumbearing lead, intermixing ktherewith a chloridizing slag, said slagrcomprising chlorine as the vchloridizing agent and melting below about '750V F., reacting said chloridizing slag with the melt to convert substantially all the indium into indium chloride, separating the slag containing indium chloride from the melt, recovering the i indium chloride from the said slagby selectiveh7 dissolving said indium chloridev in acid solution, precipitating the indium fromsolution by adding zinc, and V4chloridizingthe zincand separating 'it as ,aA slag toproducea relatively pure indium metal. Y

v9. The process of recovering Vindium from indium-bearing lead metal material containing zinc and thallium as impurities which comprises hestablishing a melt of the indium bearing material, adding a mixture of lead chloride and flux,

Vsaid Ylead chloride-ux mixtureA forming a low \meltings1ag-on top of said melt, reacting this chloridizing slag with the melt by intermixing fthe same to convert substantially all the indium Yipresentinthey meltintofindiumfchloridefrernoving the. indium chloridecontaining-'slag from the melt -by acid' leachingl said 'indium chloride: slag,

which comprise ,establishing a7 lmelt Vof .said lead .20' vcomprising lead chloride :andsodium chloride,

'-said. chloride constituents beingintroduced in proportionate amounts: such that' the resulting precipitating the indium as a4 spongy indium precipitate, digesting said aspongy metal with-caustic zincl chloride and chlorine gas to convert the zinc f chloride slag formedincluding kthe zinc andrthaland thallium present to-chlorides,separating the lium chlorides and recovering indium metal substantially free from thalliumand zincimpurities.

v10. In a process for' separating indium from impure` lead metal .containingA indium, the steps metal, .providingaslag cover for said `.melt made up .principallyof metal, chlorides, said slag, being molten `ata temperature below that at which substantial losses of .indium are incurredby volatil- .entersthe slag, andthereafter,separating the slag. containingl indium chloride', from the melt,

saidchloridizing treatment being carried outat a temperature which avoids? loss of indium ,by volatilization.

11. In a process for' separating indium'from impure lead metal containingindium, the steps which comprise establishing a melt, ofA said lead metal, providing a cover slag for said melt which is -made upk principally yoi' a mixture of lead chloride and zinc chloride, the slag melting below the temperature atwhichsubstantial losses of indiumk by volatilization occurs, intermixing the molten slagv and melt to'convert the indium constituent of the-'melt to; indium chloride which enters in the coverslag,Y said chloridizing treatment being carried out atatemperature which avoids loss of indium by volatilization, `separating the slag containing indium "chloride fromthe melt,l selectively di'ssolving'the indium chloride out of' said slag in'l an acidesolution', and'ltering the solution to remove insoluble residue and-recover' a filtrate containing indium in solution.

YURII E. LEBEDEFF.

i REFERENCES" CITED The .following references. are of, recordinlthe le of this patent: 1

UNITED Y.srs-'rus- -RATENTs `Number Name vDate '707,551 Clamer y Aug. 29, 1902 1,855,455 vMcCutcheon Apr. 26, 1932 `1,912,590 Murray .June 6,j 1933 2,082,487 Frick June 1', 1937 2,113,643 Bettertonv et a1 Apr. 12, 1938 2,119,197V Betterton et al. May 3,1, 1938 2,378,848 Heberlin June 19, 1945 '22,384,610 Doran et al Sept. 11,1945

OTHER-1REFERENCES Transactions of American Electrochemical Society, Vol. 65 (1934,), pages' 380 and' 383. Chapters in the Chemistry of Vthve'lfiess Familiar Elements, by Hopkins, vol. I1939, pages 13 and 14 of chapter'8.

vPrinciples and Applications of Electrochemistry, by W. A. Koehler, vol. II (2nd edition), 1944,- page 159. 

